Why turkey has the same name as Turkey
"very effective, almost magical remedy," 1808. The belief in the magical power of silver weapons to conquer foes goes back at least to ancient Greece (e.g. Delphic Oracle's advice to Philip of Macedon).
A very effective, quasi-magical agent, remedy, etc: Stokovich looked on Kennedy as his ''silver bullet,'' his absolute best man/ No single silver bullet is going to do the job
[1808+; reflecting an ancient belief that silver weapons can conquer any foe, found, for example, in the Delphic Oracle's advice to Philip of Macedon, ''With silver weapons you may conquer the world'']